Lecture 19 Bar Development

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Lecture 19 - Bar Development

• February 28, 2003
• CVEN 444

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Lecture Goals

• Bar Cut-off Points
• Spice

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Example- Hook
Compute the development length required for the
top 8 bar of the cantilever beam that extend
into the column support if the bars are

• Straight.
• Have a 90o hook
• Have a 180o hook

The bars are confined by 3 stirrups spaced at 6
in., and clear cover 1.5 in., and clear
spacing 2.0 in. and fc 4 ksi and fy 60 ksi
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Example- Hook straight bar
Straight bars For 8 bar db ? , because the
clear spacing 2db and clear cover is greater
than db with the bars confined condition (a) and
(b) are met. For top bars a ?
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Example- 90 oHook
Bar with 90o hook For 8 bar db ?, the basic
equation is No modification apply, than ldh
? gt 8db ? or 6 in. The factor a ? does not
apply to hooks.
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Example- 180 o Hook
Bar with 180o hook For 8 bar db ?, the
basic equation is No modification apply, than
ldh ? gt 8db ? or 6 in. The factor a ? does
not apply to hooks.
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Example Development Length
Design anchorage of 4 8 top bars in column. 4
11 bars in the transverse direction.
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Example Development Length
Try a straight bar for the development Use
12.2.2 Spacing between bars 48
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Example Development Length
The spacing ? gt db 1.0 in. So use
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Example Development Length
The coefficients need to be determined for the
reinforcement coefficient, a. There is more than
12 in. of concrete below the bar.
Uncoated bar so the coating factor is
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Example Development Length
The coefficient for aggregate is
The development length of the bar
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Example Development Length
The development of the bar going out into the
beam. Check the development length into the
column.
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Example Development Length
The clear space between the bars are
Edge
Center to center
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Example Development Length
The transverse steel area of the column is
comprised of 411 bars (As db) and the
coefficient Ktr is defined as
There are 4 transverse bars
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Example Development Length
The transverse coefficient is
There are 4 transverse bars
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Example Development Length
The transverse coefficient is
The coefficient
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Example Development Length
The development length is
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Example Development Length
Use a hook anchorage
Compute the coefficients for the column. Side
coverage
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Example Development Length
The side coverage for a 90o hook.
Top coverage is
The multiplier is ? ACI 12.5
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Example Development Length
Additional ties per ACI 12.5.4 not require only
min ties spacing gt 3 db. Multiplier is ?
The available length
The hook extension
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Example Development Length
The side coverage for a 180o hook.
The multiplier is l2
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Bar Cutoff Points
Why do you want to put in cut off points?
Economy!
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Bar Cutoff Points
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Bar Cutoff Points
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Bar Cut of Points
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Determining Locations of Flexural Cutoffs
Given a simply supported beam with a distributed
load.
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Determining Locations of Flexural Cutoffs
Note Total bar length Fully effective length
Development length
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Determining Locations of Flexural Cutoffs
ACI 12.10.3 All longitudinal tension bars must
extend a min. distance d (effective depth of
the member) or 12 db (usually larger) past the
theoretical cutoff for flexure (Handles
uncertainties in loads, design approximations,etc.
.)